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42 DESIGN007 MAGAZINE I DECEMBER 2024 From this data, the designer can assign the associated land pattern geometries and pad stack from the pre-established CAD library. To calculate the basic area required for compo- nent placement and conductor layers needed for circuit interconnect, designers must con- template the land pattern features for mount- ing the components, define "keep out zones," establish clearances reserved for assembly process evaluation, and, when necessary, post assembly rework and repair. e final analysis will provide the designer with an estimated maximum surface area needed to complete all circuit interconnects. Establishing Circuit Routing Criteria Although printed circuit board fabrication process capabilities have continued to expand on a global scale, fabrication process capabil- ity from one supplier to another, however, is not likely to be equal. is is because of the continuous advancement in related chem- istries, processing systems, materials, and overall process control evolution. Ensuring the success of the end-product's functionality requires an understanding of the designated fabricator's primar y capability attributes and how design complexity will affect the printed circuit board's producibility and cost. Following component placement, the CAD system's auto-router will assist the designer in determining the expected interconnect com- pletion rate. e auto-router function can also be used to aid the designer in identifying circuit routing bottlenecks or other critical interconnect issues not identified during the initial component placement process. If the interconnect result is less than 85%, then it is a likely indication that the designer will need to make some adjustments to component place- ment. In regard to auto-routing for frequency management applications, CAD routing tools are ver y good, but conductor routing on cir- cuit boards requiring controlled impedance or selective conductor shielding will likely require a degree of interactive manipulation by the design engineer. When component density and interconnect complexity exceed the area defined by the PCB outline, a higher level of fabrication technology will be justified, requiring additional circuit layers and/or increased conductor intercon- Table 1: Inner layer circuit routing from an independent industry capability survey